Systems and methods for transmitting a preamble within a wireless local area network (WLAN)

ABSTRACT

Some embodiments described herein provide a method for transmitting a preamble in accordance with a wireless local area network communication protocol. In some embodiments, a data frame may be obtained for transmission including a preamble compliant with the wireless local area network communication protocol. It may be determined that the preamble includes a first preamble portion that spans multiple symbol durations and a second preamble portion that spans a single symbol duration. The first preamble portion via beamforming may be transmitted based on a first beamforming matrix. When a transmission mode of the second preamble portion is beamforming, a second beamforming matrix may be generated based on the first beamforming matrix, each tone for the second preamble portion may be calculated based on the second beamforming matrix. Each calculated tone may be transmitted in accordance with the wireless local area network communication protocol.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure is a continuation of U.S. patent application Ser. No.15/262,485, filed Sep. 12, 2016, now U.S. Pat. No. 10,075,874, which inturn claims the benefit of U.S. Provisional Patent Application No.62/216,550, filed Sep. 10, 2015; and U.S. Provisional Patent ApplicationNo. 62/246,316, filed Oct. 26, 2015.

This application is related to PCT International Application No.PCT/US2016/051280, filed on Sep. 12, 2016. The aforementionedapplications are all hereby incorporated by reference in theirentireties.

FIELD OF USE

This disclosure relates to a preamble transmission mechanism in awireless data transmission system; for example, a wireless local areanetwork (WLAN) implementing the IEEE 802.11 standard, which can be usedto provide wireless transfer of data in outdoor deployments,outdoor-to-indoor communications, and device-to-device (P2P) networks.

BACKGROUND OF THE DISCLOSURE

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of theinventors hereof, to the extent the work is described in this backgroundsection, as well as aspects of the description that may not otherwisequalify as prior art at the time of filing, are neither expressly norimpliedly admitted to be prior art against the present disclosure.

Wireless local area networks (WLANs) operate under WLAN standards suchas the Institute for Electrical and Electronics Engineers (IEEE)802.11a, 802.11b, 802.11g, and 802.11n Standards. The 802.11 standardsmay specify transmission protocols and data frame formats for datapackets. For example, the 802.11 standards may adopt a physical layerconvergence procedure (PLCP), under which the PLCP protocol data unit(PPDU) format is used for preamble. The existing 802.11 PPDU in 2.4/5GHz has a mixed format structure, which includes legacy 802.11a/gportion of preambles and other format portions of preambles suitable formore recently developed 802.11 standards. Such a mixed format preambleis effective in backward compatibility and performance. Thus, because ofthe mixed structure, a transmission mechanism for the preamble is neededto adapt to both the legacy portion and the non-legacy portion, whichcan be compatible with the more recently developed 802.11 standards.

SUMMARY

Some embodiments described herein provide a method for transmitting apreamble in accordance with a wireless local area network communicationprotocol. In some embodiments, a data frame may be obtained fortransmission including a preamble compliant with the wireless local areanetwork communication protocol. It may be determined that the preambleincludes a first preamble portion that spans multiple symbol durationsand a second preamble portion that spans a single symbol duration. Thefirst preamble portion via beamforming may be transmitted based on afirst beamforming matrix. When a transmission mode of the secondpreamble portion is beamforming, a second beamforming matrix may begenerated based on the first beamforming matrix, each tone for thesecond preamble portion may be calculated based on the secondbeamforming matrix. Each calculated tone may be transmitted inaccordance with the wireless local area network communication protocol.

In some implementations, the first preamble portion includes a highefficiency short training field (HESTF), and a high efficiency longtraining field (HELTF), and the second preamble portion includes legacytraining fields and signaling configuration fields.

In some implementations, when the transmission mode of the secondpreamble portion is omni-directional, the second preamble portion may betransmitted in omni-direction with no data transmission on guard tonesthat are configured in accordance with the wireless local area networkcommunication protocol.

In some implementations, channel estimation may be performed using afirst training field contained in the first preamble portion even ifchannel estimation has been performed based on a second training fieldcontained in the second preamble portion.

In some implementations, guard tones may be filled in accordance withthe wireless local area network communication protocol with extendedsymbols.

In some implementations, the extended symbols are known symbols for areceiver to perform channel estimation.

In some implementations, at least one of cyclic delay diversity (CDD)and cyclic shift diversity (CSD) may be applied to the preamble.

In some implementations, when the CSD is applied in time domain to thesecond preamble portion, the same CSD is applied in time domain to thefirst preamble portion.

In some implementations, when the CDD is applied in frequency domain tothe second preamble portion, the same or a different CDD is applied infrequency domain to the first preamble portion.

In some implementations, the second preamble portion may be transmittedvia a mixed transmission mode of beamforming and omni-direction, whereinthe mixed transmission mode is specified via a data value transmittedwith the preamble, or implied by a transmission characteristic of thesecond preamble portion.

Some embodiments described herein provide a system for transmitting apreamble in accordance with a wireless local area network communicationprotocol. The system includes processing circuitry that is configured toobtain a data frame for transmission including a preamble compliant withthe wireless local area network communication protocol, and determinethat the preamble includes a first preamble portion that spans multiplesymbol durations and a second preamble portion that spans a singlesymbol duration. The system further includes a network interface that isconfigured to transmit the first preamble portion via beamforming basedon a first beamforming matrix. When a transmission mode of the secondpreamble portion is beamforming, the processing circuitry is configuredto generate a second beamforming matrix based on the first beamformingmatrix, and calculate each tone for the second preamble portion based onthe second beamforming matrix. The network interface is configured totransmit each calculated tone under the wireless local area networkcommunication protocol.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the disclosure, its nature and various advantageswill become apparent upon consideration of the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like reference characters refer to like parts throughout, and inwhich:

FIG. 1 is a block diagram of an example wireless WLAN 100 that thepreamble transmission mechanism can be operated within, according tosome embodiments described herein;

FIG. 2 provides an example block diagram illustrating an example of datatransmission scheme 200 for a preamble under 802.11ac, according to someembodiments described herein;

FIG. 3 provides an example block diagram illustrating an example of datatransmission scheme 200 for a preamble frame structure under 802.11ax,according to some embodiments described herein;

FIG. 4 provides an example logic flow diagram illustrating aspects oftransmitting the 1× symbol duration portion of preamble 301 and the 4×symbol duration portion of preamble/data 302, according to someembodiments described herein;

FIG. 5 provides an example block diagram illustrating a transmissionscheme 500 for the 1× symbol duration portion of a preamble (e.g., seepreamble 301 in FIG. 3), according to some embodiments described herein;and

FIG. 6 provides an example logic flow diagram illustrating a receiverprocessing a received preamble, according to some embodiments describedherein.

FIG. 7 provides an example logic flow diagram illustrating a process fortransmitting a preamble, according to some embodiments described herein.

DETAILED DESCRIPTION

This disclosure describes methods and systems for transmitting apreamble within an 802.11 wireless network. In some embodiments, thePPDU under 802.11ax may include two different portions of preamble,e.g., a 1× symbol duration portion of preamble and a 4× symbol durationportion of preamble. While the 4× symbol duration portion of preamble isusually transmitted using beamforming, the 1× symbol duration portion ofpreamble may also be transmitted via beamforming, instead of theomni-directional transmission under 802.11ac. In this way, the powerconfiguration of transmitting the two portions of the preamble of thesame PPDU may remain the same and thus do not require re-configuration.In addition, when the 1× symbol duration portion of preamble istransmitted via beamforming, data fields in both the 1× symbol durationportion of preamble and the 4× symbol duration portion of preamble canbe used for channel estimation. Also, extended symbols may be filled onthe 802.11a guard tones, which can be used to enhance channel estimationat the receiver. Thus, channel performance of the PPDU transmission maybe improved.

FIG. 1 is a block diagram of an example wireless WLAN 100 that thepreamble transmission mechanism can be operated within, according tosome embodiments described herein. A wireless access point 110 (AP)includes a host processor 105 that may be configured to process orassist in data operation, such as modulation/demodulation,encoding/decoding, encryption/decryption, and/or the like. For example,the host processor 105 may be configured to configure and/or process thedata frames illustrated in FIGS. 2-3, and/or perform the work flowsillustrated in FIGS. 4 and 6.

A network interface device 107 is coupled to the host processor 105,which is configured to interface with an outer network. The networkinterface device 107 includes a medium access control (MAC) processingunit 108 and a physical layer (PHY) processing unit 109. The PHYprocessing unit 109 includes a plurality of transceivers 111, and thetransceivers 111 are coupled to a plurality of antennas 112.

The WLAN 100 includes a plurality of client stations 120 a-c. Althoughthree client stations 120 a-c are illustrated in FIG. 1, the WLAN 100can include different numbers (e.g., 1, 2, 3, 5, 6, etc.) of clientstations 120 a-c in various scenarios and embodiments. Each clientstation, e.g., 120 a-c, may have a similar structure as that of an AP110. For example, the client station 120 c can include a host processor125 coupled to a network interface device 127. The network interfacedevice 127 includes a MAC processing unit 128 and a PHY processing unit129. The PHY processing unit 129 includes a plurality of transceivers131, and the transceivers 131 are coupled to a plurality of antennas 132to receive or transmit data from or to the wireless communicationchannel.

Two or more of the client stations 120 a-c may be configured to receivedata such as including an 802.11 PPDU 130, which may be transmittedsimultaneously by the AP 110. Additionally, two or more of the clientstations 120 a-c can be configured to transmit data to the AP 110 suchthat the AP 110 receives the data. An example data structure of apreamble under 802.11ac is illustrated in FIG. 2.

FIG. 2 provides an example block diagram illustrating an example datatransmission scheme 200 for a preamble under 802.11ac, according to someembodiments described herein. The legacy portion of the preamble mayinclude a legacy short training field (LSTF 201), a legacy long trainingfield (LLTF 202), a legacy signal field (LSIG 203), and a very highthroughput (VHT) signal field A (SIGA), which may be transmitted inomni-direction at 220. In another example, the non-legacy preamble,e.g., a preamble developed for the later version of the 802.11standards, the VHT short training field (VHTSTF 205) and VHT longtraining field (VHTLTF 206), together with the payload data 207, may betransmitted via beamforming, at 230.

Thus, the legacy portion and part of the non-legacy preamble may betransmitted in an 802.11a tone plan. For example, some of preamblefields (e.g., fields 201-204) are duplicated (e.g., see duplicatedfields 211-214, 221-224 and 231-234, which are the duplicates of fields201-204) over each 802.11a 20 MHz channel when the bandwidth is greaterthan 20 MHz. The transmission of the duplicated copies may be separatedby guard tones 245 per each 802.11a 20 MHz channel.

Due to the different transmission schemes for the omni-directionalpreamble 220 and beamformed preamble 230, additional configuration oftransmission parameters may need to be performed. For example, anLSTF-based automatic gain control (AGC) may need to be reset when thetransmission scheme switches from omni-directional to beamforming. Foranother example, the LLTF-based channel estimates obtained duringomni-directional transmission may not be for the payload datatransmission because the payload data 207 is transmitted viabeamforming. Thus, the omni-directional preamble 220 may not be usefulin the beamformed portion 230.

FIG. 3 provides an example block diagram illustrating an example datatransmission scheme 200 for a preamble frame structure under 802.11ax,according to some embodiments described herein. The 802.11ax PPDUincludes a 1× symbol duration portion of preamble 301 (tonespacing=312.5 KHz), and a 4× symbol duration portion of preamble anddata 302 (tone spacing=312.5/4 KHz). The 1× symbol duration portion ofpreamble 301 includes, in addition to the LSTF, LLTF and LSIG fields, arepeated LSIG (RLSIG 305), a high efficiency signal field A 306 (SIGA)and an HE signal field B 307 (HE-SIGB). Specifically, the HESIGB is usedto signal the resource unit signaling and physical layer (PHY)configuration for data transmission; and the HESIGA 306 provideschannel-SIGB mapping information, e.g., the information of whichchannels is carried by the HESIGB. Thus, the 1× symbol duration portionof preamble 301 is to be transmitted in a way that the 1× symbolduration portion of preamble 301 can be useful during the transmissionof the 4× symbol duration portion of preamble and data 302.

FIG. 4 provides an example logic flow diagram illustrating aspects oftransmitting the 1× symbol duration portion of preamble 301 and the 4×symbol duration portion of preamble/data 302, according to someembodiments described herein. At 401, a wireless transmitter (e.g., an802.11 transmitter) may obtain a data frame for transmission. Forexample, the data frame may be but is not limited to the 802.11axpreamble in FIG. 3. At 402, the transmitter may determine the 1× symbolduration portion of preamble (e.g., portion 301) and the 4× symbolduration portion of preamble/data (e.g., portion 302). At 403, the 4×symbol duration portion of preamble/data may be transmitted viabeamforming.

At 404, the transmission mode for the 1× symbol duration portion ofpreamble may be determined, e.g., based on a pre-defined configurationof the data frame. In one implementation, at 406, the 1× symbol durationportion of preamble 301 may be transmitted in omni-direction over802.11a tones, in a similar manner as the omni-directional portion ofpreamble 220 under 802.11ac in FIG. 2. In this way, the datatransmission may be operated in a similar manner as that in an802.11n/ac system, except that AGC may be redone using a high efficiencyshort training field (HESTF 308), and channel estimation may berestarted using a high efficiency long training field (HELTF 309).

In another implementation, the 1× symbol duration portion of preamble301 may also be beamformed with one spatial stream. For example, at 407,the beamforming matrix Q can be designed based on the 4× symbol durationportion of preamble and data 302 on the frequency domain. When multipletransmitting antennas are deployed, time domain cyclic delay diversity(CDD) may be used for antenna mapping in the frequency domain.Specifically, the j^(th) column of the training matrix A for HELTF maybe used to map a single stream to the number of spatial streams of thebeamforming matrix Q, in which j can be any available column, e.g., j=1,3, 5, . . . .

At 409, the k^(th) tone of the 1× symbol duration portion of preamble301 in the frequency domain may be calculated as:

$x_{{field},k}^{(i_{TX})} = {\sum\limits_{m = 1}^{N_{{sts},k}}{{\left\lbrack Q_{k} \right\rbrack_{i_{{TX},m}}\left\lbrack A_{field}^{k} \right\rbrack}_{m,1}s_{{field},k}{\exp\left( {{- j}\; 2\;\pi\; k\;\Delta_{F}{T_{{CS},{HE}}(m)}} \right)}}}$where denotes the k^(th) tone of the 1× symbol duration portion ofpreamble 301 at the i^(th) transmitting antenna; N_(sts,k) denotes thenumber of space-time streams at the k^(th) tone; Q_(k) denotes thebeamforming matrix on the k^(th) tone and [Q_(k)]_(i) _(TX,m) denotesthe entry on the t_(TX)-th row and m-th column; A_(field) ^(k) denotesthe training matrix for HELTF on the k^(th) tone and └A_(field)^(k)┘_(m,l) denotes the entry on the m-th row and first column;s_(field,k) denotes the data symbol being transmitted on the k^(th)tone; and Δ_(F)T_(CS,HE)(m) denotes the delay diversity factor that addsa linear phase on the k^(th) tone.

Specifically, back to 407, the beamforming matrix Q_(k) on the k^(th)tone of the 1× symbol duration portion of preamble 301 may be calculatedper each Q matrix for the 4× symbol duration portion of preamble anddata 302. The calculation may be written as:Q _(k,1×) =f(Q _(k,4×) ,k=−N _(SR) , . . . ,N _(SR))where N_(SR) denotes the number of tones. For example, the beamformingmatrix Q_(k) on the k^(th) tone of the 1× symbol duration portion ofpreamble 301 may be the same as the beamforming matrix of the 4 k-thtone on the 4× symbol duration portion of preamble and data 302, e.g.,Q _(k,1×) =Q _(4k,4×)

In another example, the beamforming matrix Q_(k) on the k^(th) tone ofthe 1× symbol duration portion of preamble 301 may be the beamformingmatrix of non-empty tone closest in frequency on the 4× symbol durationportion of preamble and data 302. Or alternatively, the beamformingmatrix Q_(k) on the k^(th) tone of the 1× symbol duration portion ofpreamble 301 may be the interpolation of the beamforming matrices on thetones around the frequency for the 4× symbol duration portion ofpreamble and data 302.

In a different example, the beamforming matrix Q_(k) on the k^(th) toneof the 1× symbol duration portion of preamble 301 may be calculated pereach Q matrix for a 4× symbol duration portion of preamble and data. Inthis way, the beamforming matrix Q_(k) on the k^(th) tone of the 1×symbol duration portion of preamble 301 is the same as that of thek^(th) tone of the 4× symbol duration portion of preamble and data.

In one implementation, at 411, when multiple transmitting antennas aredeployed, cyclic delay diversity (CDD) or cyclic shift diversity (CSD)may be applied on the frequency domain per stream. Or alternatively, CDDor CSD may be applied on the time domain per antenna. Or alternatively,a combination of both frequency-domain and time-domain CDD/CSD may beapplied.

If time-domain CSD is applied on LLTF (e.g., see field 202 in FIG. 2 orfield 311 in FIG. 3), the same time-domain CSD is also applied on anyHTLTF (high throughput LTF, not shown in the figures), VHTLTF (e.g., seefield 206 in FIG. 2), HELTF (e.g., see field 309 in FIG. 3) and the datafield (e.g., see field 320 in FIG. 3). Conversely, if time-domain CSD isnot applied on LLTF, then time-domain CSD is not applied on any of theHTLTF/VHTLTF/HELTF/data fields either.

However, frequency-domain CSD allows more flexibility. Iffrequency-domain CSD is applied on LLTF (e.g., see field 202 in FIG. 2or field 311 in FIG. 3), the same, another different or nofrequency-domain CSD is also applied on HTLTF/VHTLTF/HELTF, and the sameor the other different or no frequency-domain CSD can be applied on thedata field. If frequency-domain CSD is not applied on LLTF, afrequency-domain CSD may or may not be applied on HTLTF/VHTLTF/HELTF,and a same or different frequency-domain CSD may also be applied on thedata field.

The 1× symbol duration portion of a preamble may be defined per theirrespective purposes on each 802.11a data tone. For example, the 1×symbol duration portion of preambles may be duplicated over each 20 MHzchannel for legacy preamble, RLSIG, and HESIGA, e.g., in a similar wayas the omni-directional portion of preamble 220 is duplicated as shownin FIG. 2. The 1× symbol duration portion of preamble may be generatedby HESIGB coding.

For example, the 1× symbol duration portion of preamble symbols on the802.11a guard tones may be empty, e.g., in a similar way as shown inFIG. 2 where there is no transmission at the guard tones 245. In anotherexample, at 413, the 1× symbol duration portion of preamble symbols onthe 802.11 a guard tones may be filled with known/extended symbols,which may be filled to cover the 4× tone plan.

FIG. 5 provides an example block diagram illustrating a transmissionscheme 500 for the 1× symbol duration portion of a preamble (e.g., seepreamble 301 in FIG. 3), according to some embodiments described herein.As shown in FIG. 5, in the transmission scheme 500, the 1× symbolduration portion of preamble fields LSTF 501, LLTF 502, LSIG 503, RLSIG504, HESIGA 505, and HESIGB 506, have extended 1× preamble symbols511-516, respectively, to fill the 802.11a guard tones. The extendedsymbols 511 on LSTF may still follow the frequency density and maintainperiodicity. The extended symbols 512 on LLTF may be used for channelestimation. Alternatively, the LSIG/RLSIG/HESIGA/HESIGB extended symbols513-516 may be skipped. Power adjustment may be set on the 1× preamblesas needed.

Back to FIG. 4, at 415, the 1× symbol duration portion of preamble andthe 4× symbol duration portion of preamble/data from 403, 408 and 413,respectively, are transmitted to a receiver based on the transmissionmode configured in 403, 408 and 413.

In one implementation, the transmission of the 1× symbol durationportion of preamble may use mixed modes of omni-directional transmissionand beamforming transmission. For example, one PPDU may engage theomni-directional transmission, and the next PPDU may engage thebeamforming transmission. In this case, the mode of 1× symbol durationportion of preamble may need to be signaled.

For implicit signaling, when the HESTF does not trigger an AGC change,then the beamforming mode is applied. Or in a different example, adetection on extended symbols indicates the beamformed mode.

In another implementation, the 1× preamble transmission mode may beimplied by the frame format and/or other parameters. For example, singleuser (SU) and multi-user multiple-input multiple-output (MU-MIMO) framesmay imply that a beamformed preamble is used, and an orthogonalfrequency-division multiple access (OFDMA) frame may imply that anomni-directional preamble is used.

In another implementation, even when only a beamformed preamble is used,the receiver may treat the 1× preamble as omni-directional or beamformedbased on a decision (e.g., based on the HESTF measurement).

On the other hand, a variety of explicit signaling may be used toindicate whether a 1× preamble is omni-directional or beamformed. Forexample, the HESIGA may be configured to contain a bit to signal“omni-directional” and “beamformed” preamble mode. Or a LSIG reservedbit, or LENGTH %3 may be used to signal the preamble mode. In anotherexample, quadrature or binary phase shift keying (QBPSK) rotation may beused on a given 1× preamble symbol, e.g., HESIGA-1, HESIGA-2, or one ofthe two HESIGBs, to indicate whether the respective 1× preamble symbolis omni-directional or beamformed. In another example, a scramblingsequence on RLSIG may be used to indicate the transmission mode of therespective 1× preamble. In another example, an additional management orcontrol frame can be used to indicate the transmission mode of therespective 1× preamble. It is noted that the implicit signaling andexplicit signaling discussed above may be used independently,interchangeably, and/or jointly, when a mixed transmission mode is usedto transmit 1× preambles.

In some implementations, the HESTF field (e.g., see HESTF 308 in FIG. 3)is transmitted without regard for the transmission mode of the 1×preamble mode. Or alternatively, the HESTF data field can be skippedwhen a beamformed 1× preamble is used. In this case, some new field canbe transmitted in place of HESTF.

In some implementations, the HELTF field (e.g., see HELTF 309 in FIG. 3)is transmitted from the first column of the training matrix A. Oralternatively, the HELTF field may start to transmit with the j^(th)column of the A matrix being skipped, when using a beamformed 1×preamble and the extended preamble symbols (e.g., as shown in FIG. 4).For example, if j=1, then the HELTF field starts from the 2^(nd) columnof the A matrix.

FIG. 6 provides an example logic flow diagram illustrating a receiverprocessing a received preamble, according to some embodiments describedherein. In some implementations, at the receiver, when the 1× symbolduration portion of preamble is received at 601, the 1× symbol durationportion of preamble may be processed based on the transmission mode,which is detected at 602. For example, upon detecting a beamformed 1×preamble at 603, the receiver may skip AGC control directly at 605. Oralternatively, upon detecting beamformed 1× preamble, the receiver mayuse an LLTF (e.g., see LLTF 202 in FIG. 2 and LLTF 311 in FIG. 3) toassist an HELTF channel estimate at 605. For example, the received LLTF(e.g., field 311 in FIG. 3) and the received first symbol of HELTF(e.g., field 309 in FIG. 3) can be averaged or combined for noisesuppression. The receiver may then send the data frame to decoder at606, after the beamformed 1× symbol duration portion of preamble hasbeen processed.

The data frame transmission scheme and signaling methods discussed inFIGS. 3-6, although the different modes for 1× preamble are discussedprimarily for 802.11ax, can be extended to 802.11n/ac. For example, theimplementations discussed in connection with any of the HE fields canalso be applied on the corresponding HT/VHT field. The 11n/11acomni-directional preamble can also be transmitted in beamformed mode.The preamble mode may also be signaled either implicitly or explicitlyas described for 11ax. For example, all implicit signaling methodsdiscussed in connection with 802.11ax can be applied for 11n/ac.Explicit signaling can be done by setting reserved bits in LSIG, HTSIG,VHTSIGA, or by setting certain fields to a specific value.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of what may be claimed, but,rather, as descriptions of particular implementations of the subjectmatter. Certain features that are described in this specification in thecontext of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can, in some cases, beexcised from the combination, and the claimed combination may bedirected to a subcombination or variation of a subcombination.

While operations are depicted in the drawings in a particular order,this should not be understood as requiring that such operations beperformed in the particular order shown or in sequential order, or thatall illustrated operations be performed, to achieve the desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the aspects described above should not be understood asrequiring such separation in all aspects, and it should be understoodthat the described program components and systems can generally beintegrated together in a single software product or packaged intomultiple software products.

Suitable computer program code residing on a computer-readable mediummay be provided for performing one or more functions in relation toperforming the processes as described herein. The term“computer-readable medium” as used herein refers to any non-transitoryor transitory medium that provides or participates in providinginstructions to a processor of the computing device (e.g., the BLEdevice 106 a-b, the receiving server 105, or any other processor of adevice described herein) for execution. Such a medium may take manyforms, including but not limited to non-volatile media and volatilemedia. Nonvolatile media include, for example, optical, magnetic, oropto-magnetic disks, or integrated circuit memory, such as flash memory.Volatile media include dynamic random access memory (DRAM), whichtypically constitutes the main memory. Common forms of computer-readablemedia include, for example, a floppy disk, a flexible disk, hard disk,magnetic tape, any other magnetic medium, a CD-ROM, DVD, any otheroptical medium, punch cards, paper tape, any other physical medium withpatterns of holes, a RAM, a PROM, an EPROM or EEPROM (electronicallyerasable programmable read-only memory), a FLASH-EEPROM, any othermemory chip or cartridge, or any other non-transitory medium from whicha computer can read.

The subject matter of this specification has been described in terms ofparticular aspects, but other aspects can be implemented and are withinthe scope of the following claims. For example, the actions recited inthe claims can be performed in a different order and still achievedesirable results. As one example, the processes depicted in theaccompanying figures do not necessarily require the particular ordershown, or sequential order, to achieve desirable results. In certainimplementations, multitasking and parallel processing may beadvantageous. Other variations are within the scope of the followingclaims.

What is claimed is:
 1. A method for transmitting a preamble inaccordance with a wireless local area network communication protocol,the method comprising: obtaining a data frame for transmission compliantwith the wireless local area network communication protocol; determiningthat the data frame includes a first preamble portion and a secondpreamble portion; transmitting the first preamble portion viabeamforming based on a first beamforming matrix; and determining whethera transmission mode of the second preamble portion is beamforming in asame way as the first preamble portion or omni-directional based on atype of the wireless local area network communication protocol; inresponse to determining that the transmission mode of the secondpreamble portion is beamforming in the same way as the first preambleportion: transmitting the second preamble portion via beamforming basedon the first beamforming matrix.
 2. The method of claim 1, wherein thetransmitting the second preamble portion via beamforming based on thefirst beamforming matrix comprises: generating a second beamformingmatrix based on the first beamforming matrix; calculating each tone froma plurality of tones used to transmit the second preamble portion basedon the second beamforming matrix; and transmitting each calculated tonein accordance with the wireless local area network communicationprotocol.
 3. The method of claim 1, wherein the second preamble portionincludes a legacy portion and a high-efficiency (HE) portion, andwherein the HE portion includes a HE-SIGA field, and the method furthercomprises: configuring a bit in the HE-SIGA field to indicate that thebeamforming remains unchanged between the legacy portion and the HEportion.
 4. The method of claim 1, further comprising: when thetransmission mode of the second preamble portion is omni-directional,transmitting the second preamble portion in omni-direction with no datatransmission on guard tones that are configured in accordance with thewireless local area network communication protocol.
 5. The method ofclaim 4, further comprising: performing channel estimation using a firsttraining field contained in the first preamble portion even if channelestimation has been performed based on a second training field containedin the second preamble portion.
 6. The method of claim 1, furthercomprising: filling guard tones in accordance with the wireless localarea network communication protocol with extended symbols, and whereinthe extended symbols are known symbols for a receiver to perform channelestimation.
 7. The method of claim 1, further comprising: applying atleast one of cyclic delay diversity (CDD) and cyclic shift diversity(CSD) to the preamble.
 8. The method of claim 7, wherein: when the CSDis applied in time domain to the second preamble portion, the same CSDis applied in time domain to the first preamble portion.
 9. The methodof claim 7, wherein: when the CDD is applied in frequency domain to thesecond preamble portion, the same or a different CDD is applied infrequency domain to the first preamble portion.
 10. The method of claim1, further comprising: transmitting the second preamble portion via amixed transmission mode of beamforming and omni-direction, wherein themixed transmission mode is specified via a data value transmitted withthe preamble, or implied by a transmission characteristic of the secondpreamble portion.
 11. A system for transmitting a preamble in accordancewith a wireless local area network communication protocol, the systemcomprising: processing circuitry configured to: obtain a data frame fortransmission compliant with the wireless local area networkcommunication protocol, and determine that the data frame includes afirst preamble portion and a second preamble portion; and a wirelesstransmitter configured to transmit the first preamble portion viabeamforming based on a first beamforming matrix; wherein the processingcircuitry is further configured to determine whether a transmission modeof the second preamble portion is beamforming in a same way as the firstpreamble portion or omni-directional based on a type of the wirelesslocal area network communication protocol, and in response todetermining that the transmission mode of the second preamble portion isbeamforming in the same way as the first preamble portion, the wirelesstransmitter is further configured to transmit the second preambleportion via beamforming based on the first beamforming matrix.
 12. Thesystem of claim 11, wherein the processing circuitry is furtherconfigured to: generate a second beamforming matrix based on the firstbeamforming matrix, and calculate each tone from a plurality of tonesused to transmit the second preamble portion based on the secondbeamforming matrix; and wherein the wireless transmitter is configuredto transmit each calculated tone in accordance with the wireless localarea network communication protocol.
 13. The system of claim 11, whereinthe second preamble portion includes a legacy portion and ahigh-efficiency (HE) portion, and wherein the HE portion includes aHE-SIGA field, and the processing circuitry is further configured to:designate a bit in the HE-SIGA field to indicate that the beamformingremains unchanged between the legacy portion and the HE portion.
 14. Thesystem of claim 11, wherein the wireless transmitter is furtherconfigured to: when the transmission mode of the second preamble portionis omni-directional, transmit the second preamble portion inomni-direction with no data transmission on guard tones that areconfigured in accordance with the wireless local area networkcommunication protocol.
 15. The system of claim 14, wherein theprocessing circuitry is further configured to: perform channelestimation using a first training field contained in the first preambleportion even if channel estimation has been performed based on a secondtraining field contained in the second preamble portion.
 16. The systemof claim 11, wherein the processing circuitry is further configured to:fill guard tones in accordance with the wireless local area networkcommunication protocol with extended symbols, and wherein the extendedsymbols are known symbols for a receiver to perform channel estimation.17. The system of claim 11, wherein the processing circuitry is furtherconfigured to: apply at least one of cyclic delay diversity (CDD) andcyclic shift diversity (CSD) to the preamble.
 18. The system of claim17, wherein: when the CSD is applied in time domain to the secondpreamble portion, the same CSD is applied in time domain to the firstpreamble portion.
 19. The system of claim 17, wherein: when the CDD isapplied in frequency domain to the second preamble portion, the same ora different CDD is applied in frequency domain to the first preambleportion.
 20. The system of claim 11, wherein the wireless transmitter isfurther configured to: transmit the second preamble portion via a mixedtransmission mode of beamforming and omni-direction, wherein the mixedtransmission mode is specified via a data value transmitted with thepreamble, or implied by a transmission characteristic of the secondpreamble portion.